1. Technical Field
This invention relates to aircraft gas turbine engines and, particularly, to borescope inspection ports on gas turbine engines.
2. Background Information
Borescope inspection ports are commonly used on aircraft gas turbine engines. Borescope ports allow visual inspection of internal aircraft engine flowpath hardware with a fiber optic borescope. These borescope ports make possible frequent engine inspections that otherwise could not be performed without disassembly of the aircraft engine. This allows increased engine usage between overhaul and, thus, lowers aircraft engine operating costs. During engine operation, borescope plugs are used to close the inspection ports on the engine and prevent the escape of high pressure engine gases. Conventional borescope plugs typically close an outer port through an engine casing and seals a flowpath structure such as a turbine blade shroud at an inner port. A spring loaded plunger seals against the inner port. A bolt head is provided for assembling and disassembling the plug from a threaded mount on the engine casing.
Borescope plugs are used to plug the inspection ports used during borescope inspections of hot sections of the engine such as the high pressure turbine (HPT). An exemplary borescope plug and inspection ports are disclosed in U.S. Pat. No. 4,815,276 and incorporated herein by reference. The plugs have to endure the harsh environment near the hot turbine flowpath, while being made out of less capable materials than other parts near the flowpath in the HPT. Since the plug does not extend all the way to the flowpath, a cavity is formed in the port below or radially inward of the plug. This cavity entraps hot flowpath air resulting in high metal temperatures on the port walls and a tip of the plug. Overheating of the port and the tip due to stagnating hot air entrapped by the cavity can cause premature deterioration of the port and the tip requiring expensive repairs. Thus, it is highly desirable to have to provide low cost and effective cooling of both the plug tip and the port.